Precision spraying of viscous fluids

Click here to learn more about viscosity measures and the effects of viscosity on fluid properties. 

Viscous fluids can be tricky to spray with simple hydraulic nozzles.The more viscous a fluid, generally speaking, the lower the spray angle will be. A spray angle of 90° for water, for example, may only provide a 60° angle for a more viscous fluid. You can increase the pressure but, with simple hydraulic nozzles, this affects flow rate which affects the spray pattern, causing overspraying.

Electronically actuated nozzles

With electronic nozzles, we can actually compensate for this in to some degree by using pulse-width modulation (PWM) - we can spray at those higher pressures and, if we're overspraying due to the higher pressure and resulting higher flow rate, we can pulse the nozzle on and off very, very rapidly. 

However, electric nozzles are limited in the pressures they can spray at and will not cope at much above 20 bar.  They can therefore not spray fluids much above 25 centipoise.

Air atomising nozzles

Air atomising nozzles use the energy in compressed air or gas to produce finely atomised liquid sprays at relatively low operating pressures. When a viscous fluid needs to be sprayed/atomised and cannot be sprayed with a hydraulic single-fluid nozzle, a two-fluid air atomising design is often the best option. The XA10 & XA11 low flow nozzle systems can be used with FlexFlow™ to achieve a variety of air atomising spraying objectives, with a choice of internal or external mix set-ups.

For fluids much above 100cps (about the thickness of double cream), however, problems occur with internal mix nozzles.  The larger droplet sizes and bubbles that form in the chamber severely impede the spray formation.  This can lead to blockages and a severely degraded spray pattern.  To overcome this problem, external mix air atomisers should be deployed. These mix the air with the fluid stream after exit from the nozzle and so will not encounter the problems faced by internal mix atomisers.


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